A Long-Term Evolution (LTE) system offers high peak data rates, low latency, improved system capacity, and low operating cost resulting from simplified network architecture. LTE systems also provide seamless integration to older wireless network, such as GSM, CDMA and Universal Mobile Telecommunication System (UMTS). In LTE systems, an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of base stations, e.g., evolved Node-Bs (eNBs) communicating with a plurality of mobile stations referred as user equipments (UEs).
Scheduling Request (SR) is a request of scheduling radio resource for uplink (UL) transmission by the UE to the eNB. The SR informs the eNB that the UE has new data to transmit. There are two types of SR transmission: dedicated SR (D-SR), where the SR is conveyed on a dedicated resource such as physical UL control channel (PUCCH), and random access-based SR (RA-SR), where the SR is conveyed on a contention channel such as random access channel (RACH).
Carrier aggregation (CA)/radio resource aggregation is introduced to improve system throughput. With carrier aggregation, the LTE-Advance system can support higher data rate. Such technology is attractive because it allows operators to aggregate several smaller contiguous or non-continuous component carriers (CCs) to provide a larger system bandwidth, and provides backward compatibility by allowing legacy users to access the system by using one of the component carriers. LTE also allows carrier aggregation from different eNBs. Different from the traditional wireless system, with inter-eNB or inter-RAT carrier aggregation, the UE needs to associate with multiple schedulers from different base stations. For inter-BS carrier aggregation, the base stations providing the carrier components are not physically collocated, it requires transmission medium and interfaces among the base stations. However, in a real deployed system, the exchanging of information among base stations is limited by the backhaul delay and additional overhead. Therefore, to increase the flexibility and efficiency in uplink scheduling, the UE needs to be able to associate to individual schedulers in each base station. Each base station should have its own private access channels for SR, channel station information (CSI), HARQ feedback and other functions to provide instantaneous assistant for dynamic scheduling. Accordingly, the UE should have additional functions to handle communicating and coordinating with multiple schedulers from different base stations, which belong to the same or different RAT.
Improvements and enhancements are required for UE SR procedures to communicate and manage multiple schedulers from different base stations.